Weatherspoon, who was drafted 19th overall in 2010, emerged as the key to coordinator Mike Nolan's defense as a sideline-to-sideline force, trying for the team lead with 95 tackles last season despite missing three games. An every-down player, Weatherspoon has defended 13 passes and collected eight sacks in his career.

With Weatherspoon now sidelined for at least eight weeks, coach Mike Smith and general manager Thomas Dimitroff will turn to two undrafted rookies who impressed this summer, Delaware product Paul Worrilow and Texas State's Joplo Bartu. Both impressed with their versatility and athleticism.

The Falcons apparently have no plans to re-sign linebacker Brian Banks, who spent training camp and preseason with the team and participated in his first football games since a wrongful rape conviction derailed his once-promising career in high school. Banks' agent, Ryan Tollner, confirmed to USA TODAY Sports on Tuesday that Atlanta has not reached out despite losing Weatherspoon.

The team, however, did sign veteran free-agent linebackers Jamar Chaney and Omar Gaither, who were initially drafted by the Philadelphia Eagles. Chaney played in 44 games with 23 starts in three seasons with Philadelphia.

Gaither posted 321 tackles, six sacks and two interceptions in seven seasons during stints with the Eagles, Carolina Panthers and Oakland Raiders.

The club also signed free-agent fullback Patrick DiMarco, who started four games for the 2012 Kansas City Chiefs.

Jackson, 30, the team's primary offseason acquisition was hurt Sunday while scoring a touchdown against the St. Louis Rams. Expect Jacquizz Rodgers and Jason Snelling to pick up the load in Jackson's absence.